Hammer control circuit in high speed printers



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llil llllnlllll United States Patent 3,185,076 HAMMER CGNTROL CERQEHT IN ESE SEED PRINTERS;

Frederick E. Booth, J12, Birmingham, Mich, assignor, by mesne assignments, to Control Data Corporation, Mimeapoiis, Minn a corporation of Minnesota Fiied Sept. 13, 1961', Ser. No. 138,313 Qiaims. (Ci. 1ii193) This invention relates to printers for use with electronic computers, and particularly to a novel electro-mechanical, so-called on-the-iiy type printer such as fully disclosed in application Serial No. 138,157. More specifically, this invention relates to a hammer magnet control system for synchronizing the operation of the printer hammers and for sequencing the printer operation.

Very briefly, a printer embodying the invention includes a continuously rotated print drum having characters spaced radially around the drum in horizontal rows of identical characters to be printed. Printing takes place by causing hammers to drive the paper into the characters on the drum.

The printer disclosed herein may be used in conjunction with a computer-buffer combination as a medium and/or high speed data processing system. For eX- ainple, the particular embodiment of the printer disclosed herein is capable of printing 12%? character lines at a rate of 150 lines per minute, and under special circumstances at a rate of 680 lines per minute for all numeric characters. The computer derives the necessary information and places it on its output terminals in such a way that it is fed into the printer one line at a time. After the computer has completed the derivation of one line of information, it then derives the vertical format or number of lines which the computer desires to skip on a printed sheet before it prints the next line. This I-.-ormation is also fed out onto the computer output lines and used by the printer.

Before stating some of the specific objects of the invention and describing the construction and operation of the printer in detail, it seems desirable to present a general discussion thereof for purposes of orientation. this connection, the assumption will be made that e computer with which this printer is employed sorts 'nforrnation in terms of character bins. In other words, as the computer looks at information in its arithmetic re 'ster system, it determine two things about a particular character of information. First, it determines what character it wishes to print; second, it determines at what address or hammer number from 1 to 120 it wishes to this character. A portion of the memory in this printer has been designated for the addresses of each character. Since this particular embodiment of the printer is designed to print no more than 12 characters on any given line, 120 positions in memory have con assigned for addresses of each character, either alphan meric or numeric, which it is desired to print.

After the corn uter has processed the information which it wishes to print and has placed all addresses in their appropriate character bins, the computer is then prepared to output this information to the printenbuffer combination. When the computer is in its print mode of operation, it receives information from the printer telling it which character the printer is capable of printing. The computer then sorts through the appropriate bin, locating the addresses of all positions which the computer desires to print. These addresses are fed in sequence through the buffer, amplified and impedance matched by the buffer and then fed to the input register of the printer. The printer input register decodes the computer signals and pulses appropriate hammer mag- "ice nets, causing the selected hammers in the printer to be triggered and dropped into a print cam so as to print the character.

After the computer has determined that one complete line of information has been sent to the printer, it then determines the vertical format or number of lines to be skipped the printed form before the next line is printed. This skip information is then placed on the output lines of the computer, reduced by the buffer, and sub sequently fed into the input register of the printer. At the end of the paper skip period, the printer feeds an input request signal back to the computer telling the computer that it i ready to print the next line of information. The computer then reduces the next line of information, repeats the pevious sequence of accepting characters to be printed from the printer, and places the addresses of these characters on the output lines of the computer to be fed into the input register of the printer.

in most instances, a computer such as that presently under discussion for orientation purposes Will be connected through its input-output lines to several pieces of equipment in addition to the printer. This other equipment may be tape readers, card readers, tape punches, or perha another computer. As the computer attempts to communicate with any one of the several units of such peripheral equipment attached to it, there is the possibility of causing malfunction in one of the other pieces of equipment. Steps must therefore be taken to insure that only the selected piece of equipment is able to send or receive information. Thus, the buffer referred to above is placed between the computer and the printer to insure that no information is received from the printer and that no information is fed into the printer input register, except at times when the printer has been selected by the computer as an output device. The buffer accomplishes this function by controlling the gating of both the computer input to the address register and the printer output from the character generator. The buffer detects the printer select code from the computer and uses this code to enabie or inhibit the gates in the bufier system. in addition to accomplishing the gating function, the buffer also serves as an impedance matching device between the output of the computer and the input to the printer, and between the output of the printer and the input of the computer.

The printer is designed to be a general purpose device that can adapt itself to most types of computers. However, cases occur where the printer cannot directly use either the wave shapes or the voltage levels which may be placed on the computer output line. In these cases, pulse forming and gating networks in the buffer are used to re-shape the pulses. S ecific illustrations are the strobe line, which must be delayed from the computer information ready line, and the paper advance command, which is derived from the computer paper advance command but is re-shaped. The printer input register reset command is also derived in the buffer from computer output.

As will be seen from the subsequent detailed description, the specific printer disclosed herein involves the use of certain magnets associated with each print hammer, and a basic objective in the design of this printer is to energize the correct print magnets at the proper time to enable the selected hammers to fall into a print cam and be driven against the proper character on the print drum. The selection of one of the print magnets is accomplished by the computer input decoding system, which uses the address placed on the input lines by the computer to set a group of input flip-flops, seven in this particular printer design. These seven printer input flip-flops are used in conjunction with a double level gatin system to define one of 120 unique print positions. When the seven computer input lines define one print magnet, this input signal causes a circuit called a print magnet thyristor to be turned on through a resistor. Turning on the thyristor allows selection of the proper print magnet.

Synchronization between release time or the print hammer associated with the triggered print magnet and a mechanical print cam is accomplished through use of a variable reluctance magnetic piclrup. This magnetic pickup senses the position of the lobes formed on the print cam and is used to trigger the printer control timer. The printer control timer is an interrelated group of one-shot multiviorators that determines the length of each portion of one print cycle. A print cycle is defined as the time required for succeeding rows of identical characters on the print drum to pass a fixed line, such as the line of print hammers; in the particular printer disclosed, it covers a period of 6.25 milliseconds.

The above print cycle is itself divided into three different times referred to herein as the reset time, the read time, and the type command time. More specifically, the reset time is a period of one-half millisecond following detection of a lobe on the print cam; durin" this period, the thyristors, which control the 120 print magnets and have been previously energized, are simultaneously turned ott or put at zero position. 1

During the next two milliseconds, the read time, a printer input request signal is generated by the control timer. This printer input request signal is processed through the buffer and fed into the computer, telling the computer, so to speak, that during these two milliseconds, time is available to feed the addresses of particular char.- acters into the printer. The computer then scans the printer character generator for the character on the print drum approaching the print hammer positions and places the addresses of all positions for this character in storage on the computer output lines. During this two millisecond printer input request or read time, all the thyristors at hammer positions called for by the computer are thus energized.

The following 3.75 milliseconds of the print cycle, the type command time, are taken up by the print magnet power period or type command. During this time, a high current pulse is gated to all hammer magnets whose thyristors have previously been selected. At the end of the 3.75 millisecond type command period, all hammers requested by the computer will have been positioned in the path of the print cam. The next cam lobe is then sensed by the magnetic pickup, and a new reset signal is generated to turn off all thyristors in the unit.

The paper moving means employed in this printer includes a solenoid controlled spring clutch. Thus, in addi tion to energizing the proper print magnet at the proper time, another basic objective of this printer design is to energize the spring clutch solenoid at the proper time and for the proper length of time. In this case, the length of time is important. A millisecond input signal to the spring clutch solenoid will result in paper motion of one line; energizing the clutch for multiples of 10 milliseconds will result in multiple line skip. In the present system configuration, the spring clutch solenoid is fed with two levels of signal, a first high power system and a second low power system. The first level of signal is a high current 10 millisecond signal insuring that the solenoid, and thus the spring clutch, is energized rapidly and positively and resulting in paper motion of one line; the second input in a paper vertical format control of lower level which may be sustained for continuous duty and which will cause the spring clutch to continue to be energized, although it may not insure actuation of the spring clutch. When single line skip mode is required, the vertical format control system will not be energized; where multiple line ship is required, the computer will feed a paper skip signal into the input decoding system, the skip signal being subsequently decoded and used to energize one of eight printer OR gates.

The vertical format control is a photodiode system comprising an eight channel photodiode paper tape read mechanism, the paper tape motion being mechanically synchronized with the motion of the paper drive spring clutch. Actually, there are nine photodiode channels, but one is used for strobe. Each of the other eight channels of the paper tape may comprise a commonly used print format. By gating together one of the eight printer AND gates selected by the input decoding system and the eight channels of output from the vertical format control photodiode system, it is possible to select one of eight commonly used paper formats with the computer. The selected channel is then fed into the paper vertical format control system and is used to stop paper motion at the appropriate time.

The printer includes a print drum character generator comprising a code disk photodiode system. The code disk is mechanically fastened to the print drum mecha' nism, and it generates a parallel character synchronized with the character on the print drum. The output of these photodiodes are amplified and impedance matched in the butter and gated to the computer at all times when the butter is in the printer select mode.

it has already been stated that the printer under consideration is designed to print a maximum of characters per line and that it involves the use of magnets associated with the print hammers. Actually, the printer contains 120 polarized magnets, called hammer electromagnets, associated with print positions 1 through 120. Each electro-magnet has two windings, a holding coil winding and a pulse coil winding. The holding coil winding is continuously energized during operation of the printer and has sufficient strength to hold a print hammer interposer system, which includes an actuator lever having an armature, clear of the print cam. The pulse coil is Wound on the same bobbin with the holding coil. The ampere turns of the pulse coil exceed those of the holding coil, and they are so sensed when energized that they oppose the force of the holding coil, thus freeing the print hammer armature and enabling the print hammer to be operated by the print cam each time a pulse coil is energized. All of the 120 pulse coils are driven in parallel by a type command power amplifier, but only hammers selected by the hammer magnet trigger. gate system will be printed.

As already explained, the synchronizing magnetic pickup referred to above senses the time at which a particular character is beginning to appear beneath the hammer and resets all pulse coil thyristors, reset occupying 0.5 millisecond. During the next two milliseconds of the print cycle, the printer is prepared to receive the address of all hammers which the computer desires to print on the particular character beneath the hammers. It is during the remaining 3.75 milliseconds of the print cycle, that power is applied to all of the pulse coils in parallel, and any hammers which have been thus selected during the input request period will be released into the print cam.

While type command power is applied to all pulse coils, only selected pulse coils will be energized. The electrical circuit is completed from a type command power amplifier buss, through the selected pulse coil and then through the thyristor of the selected units to ground. The thyristor is a semiconductor device having characteristics similar to those of a vacuum tube thyratron. The thyristor may be turned on with a low level short duration signal on the base, but it must be turned off by reducing thyristor circuit current to a level which is less than the device sustaining current. Turn oil of all thyristors is accomplished in parallel by driving both the reset bus and the type command power amplifier bus to 6 volts simultaneously for a period of 0.5 milliseconds. Each thyristor may be selected and turned on in less than 7 microseconds, and all 120 thyristors may thus be serially selected in appreciably less than the 2 milliseconds of input request time. The reset power amplifier bus is driven by a transistorized emitter follower system; the emitter follower, in turn, is driven by a 0.5 millisecond reset bus control one-shot multivibrator, the multivibrator being triggered by the synchronizing magnetic pickup. The type command power amplifier bus is driven by a transistorized emitter follower system which in turn is driven by a type command control flip-flop. The type command control flip-flop is set by the trailing edge of the signal from the printer input request one-shot multivibrator, and it is reset by the leading edge of the signal from the reset bus one-shot multivibrator. The printer input request one-shot multivibrator is triggered by the trailing edge of the reset signal and switches for 2 milliseconds, feeding a signal back to the computer-buffer systern which may or may not be difierentiated.

All thyristors are reset or turned off at the beginning of a print cycle by causing the printer reset command and the printer type command buses to simultaneously go to volts, reducing the current through the thyristors below the sustaining current level. During the following 2 milliseconds, voltage will be applied to the thyristor collector through the printer reset command and buss, but no voltage will be applied to the hammer magnet pulse coils through the printer type command buss. This allows the thyristors to be selected and turned on into a non-inductive load in serial order, and it insures that all hammer magnet pulses are of equal length. Turn off or leakage current is supplied to the base of the thyristor through a resistor to the power supply. Turn on current is supplied through an isolated diode by a resistor-capacitor network connected to the computer input decoding system.

Referring again to the computer input decoding system consisting of seven printer input flip-flops which receive and store the address of the particularly character that the computer wishes to print, the state of the seven input flip-flops is used to define one of the 120 unique hammer positions through the two level gating system. The true and prima sides of the first three flip-flops are used to drive eight diode AND gates; the outputs of the other four flip-flops are used to drive fifteen OR gates. The product of the fifteen OR gates and the eight AND gates are used to drive the resistor-capacitor input networks to 120 hammer magnet thyristors.

It is possible that the switching speeds of the seven input flip-flops are not identical. If the transient signals during the set and reset time of these flip-flops is allowed to propagate through the gates, a hammer may be erroneously selected. The gate system is therefore inhibited by a strobe signal during input flip-flop set and reset times. This strobe is derived by the buffer and fed through the strobe or matrix trigger input amplifier to a fourth input on each of the eight AND gates. The thyristor requires a negative going base current of 5 milliamperes for a period of 150 microseconds to ensure turn on. This base current is derived by charging the input capacitor at a slow rate for a minimum of 6 microseconds, and discharging the input capacitor through the thyristor base for a minimum of 150 millimicroseconds. Gate current requirement during the capacitor charge cycle is low due to the large input network series resistor. Gate current requirement is also low during the capacitor discharge cycle, due to the fact that only one of the 120 input capacitors has been charged, and must therefore be discharged. The outputs of both the AND and the OR gates are either 0 or plus 10 volts. The combination which produces triggering of the thyristor is a 0 voltage out of the OR gate and plus 10 volts out of the AND gate; this causes the thyristor input capacitor to be charged to 10 volts, with the minus polarity facing the thyristor input diode. When the AND gate potential switches from plus 10 to 0 volts, the capacitor discharges through the base of the thyristor, causing the device to turn on.

When the computer-buffer system determines that all required information has been printed on one particular line of the data sheet, the start paper advance input signal will be generated and fed into the printer. It is possible, in the case of some computer-buffer systems, for this start paper advance signal to be derived and sent to the printer before the mechanical operation of completing printing has been finished. When the printer receives a start paper advance signal and the spring clutch causes the paper motion mechanism to start while print hammers are still striking the paper, the paper feed holes may be elongated or torn. To prevent this, a start paper advance delay one-shot multivibrator is inserted between the start paper advance input and the start paper advance control multivibrator; this delay insures that print hammer motion will have been completed before paper motion begins.

The inertia in the paper drive mechanism is sufficient so that a damped oscillation takes place at completion of paper advance; if hammers are allowed to fall on the paper during this oscillation time, haloeing or deterioration of print quality may occur. Accordingly, a printer input request inhibit signal is sent to the computerbuifer system to prevent input to the printer until paper motion has been damped out. The printer input request inhibit signal is derived by monitoring the high power and low power paper drive systems and using the end of the paper drive signal to trigger a printer input request inhibit one shot multivibrator. The delay inherent in this multivibrator insures that no print signals are received until paper motion has been mechanically damped out.

The high power paper drive amplifier is a conventional, common-emitter power amplifier driven by an emitter follower power amplifier which in turn is driven by a ten millisecond start paper advance one shot multivibrator. The start paper advance input causes a ten millisecond power pulse to appear across the spring clutch control solenoid. This pulse is long enough to insure actuation of the spring clutch system long enough to insure one line of paper advance, but not long enough to allow two lines of paper advance. When the printer is in the multiple line ship mode and the clutch control solenoid is hein energized by the low power paper drive amplifier, the time at which the solenoid is de-energized to stop paper advance is very critical. For a given number of lines of paper skip, if the electrical signal to de-energize the solenoid is given too soon, one line too few of paper advance will result; if the electrical signal is given too late, one more line of ship than is requested byv the con puter will result.

To insure that the control solenoid energization is properly synchronized, the electrical signal to the low power paper drive amplifier system is derived from the vertical format control photodiode system. The vertical format control photodiode system comprises an eight channel photodiode block, a punched paper tape transport mechanism mechanically connected to the printer paper motion mechanism and a light-lens system to illuminate the photodiodes.

The low power paper drive system, which is used to maintain the spring clutch control solenoid energized during multiple line skip, is driven by a paper drive format control flip-flop. This flip-flop is set by the same start paper advance input signal which energizes the high power paper drive one shot multivibrator. When the printer is in the signal line skip mode, both the start paper advance one shot multivibrator and the paper drive format control flip-flop are energized, giving both high power and low power paper drive signals to the spring clutch solenoid. However, the paper drive format control flip-flop is reset by the stop paper advance signal before completion of one line or" paper advance. In the .2 multiple skip mode, both high power and low power paper drive systems are energized by the start paper advance input. The stop paper advance signal, which resets the paper drive format control flip-flop, is derived from a selected channel of the vertical format control photodiode system. Selection of this channel may be accomplished in one of two ways: A manual switch may be used, or one of the eight photodiodes channels may be selected by the computer-buffer system and gated to the stop paper advance AND gate. In this way, the signal which controls the number of lines of paper skip is derived from a system that is mechanically coupled to the paper drive mechanism, which insures that the paper stop signal arrives at the printer electronics in proper time sequence. A change of paper tape in the reader allows a maximum of flexibility in selection of paper format.

It will be understood, of course, that the specific voltage and current values and the times stated in the above gen eral discussion are given mainly for the purpose of indicating the mode of operation; that is, they are not in any way intended to be limiting, it being apparent that the printer design could be varied in this respect.

Inasmuch as the print drum is continuously rotated at a relatively high speed and a line of print is completed on a single revolution of the print drum, it is apparent that the print hammer mechanism must necessarily be capable of extremely rapid operation. At the same time, however, the hammer mechanism must give printing of uniform intensity and spacing, be relatively easy to assemble and repair and be dependable in operation.

From the above general discussion of the printer, it is apparent that one of the objects of the invention is to provide a printer for use with electronic computers or the like having an improved hammer control system.

Another object of the invention is to provide a printer hammer control system including means for cycling the hammers through a reset time, an information request time, and print command time.

Another object of the invention is to provide a printer hammer control system as set forth above wherein the cycle time of the hammers is 6.25 milliseconds with the reset time, information request time and print command time are .5, 2 and 3.75 milliseconds respectively.

Another object of the invention is to provide a printer hammer control system as set forth above and including a disk rotatable at the speed of the printer print drum and having magnetic members spaced angularly around the circumference thereof, and an electromagnetic probe positioned adjacent said disk operable to develop an electric pulse each time one of the magnetic members in the disk rotates thereby for synchronizing the operation of the eleotronicand mechanical portions of the printer.

Another object of the invention is to provide a printer hammer control system as set forth above wherein the means for cycling the hammers through a reset time includes a one-shot multivibrator and an amplifier connected to receive pulses from the electromagnetic probe and to generate a reset signal for a predetermined time which reset signal is applied to the separate thyristors associated with each printer hammer. 7

Another object of the invention is'to provide a printer hammer control system as set forth above wherein the means for cycling the hammers through an information request time comprises a first one-shot multivibrator connected to provide a signal to a second one-shot multivibrator a predetermined time after an electric pulse from the electromagnetic probe is sensed by the first multivibrator whereby the second multivibrator is placed in a state of operation to provide a read out enable signal for a predetermined time.

Another object of the invention is to provide a printer hammer control system as set forth above wherein the means for cycling the hammers through a print command 8 time comprises a third one-shot multivibrator operable only after receiving an electric pulse from the second multivibrator after the information request time to provide a signal to the separate thyristors associated with each printer hammer to cause the thyristors to conduct heavily through the hammer pulse coils.

Another object is to provide a printer hammer control system which is simple in construction, economical to manufacture and efficient in use.

These and other objects and advantages of the invention will become apparent by reference to the following specification and the accompanying drawings, wherein:

FIGURE 1 is a perspective view of a printer embodying the invention;

FIGURE 2 is a cross-sectional view, with portions thereof cut away, taken on the plane of line 22 of FIG- URE 1 and looking in the direction of the arrows;

FIGURE 3 is an end elevational view showing the magnetic signal generator in the printer;

FIGURE 4 is a perspective view or" a group of print hammers, their interposer linkages and the means for addressing the same;

FIGURE 5 is a block diagram illustrating a representative computer with which the printer may be used;

FIGURE 6 is a block diagram illustrating a representative buiier which may be used between the computer illustrated in FIGURE 5 and the printer;

FIGURE 7 is a block diagram illustrating the electronic portion of the printer;

FIGURE 8 is a partly block and partly schematic diagram illustrating the hammer magnet control system of the electronic portion of the printer;

FIGURE 9 is a partly block and partly schematic diagram illustrating the hammer magnet gate system of the electronic portion of the printer;

FIGURE 10 is a partly block and partly schematic diagram illustrating the paper motion spring clutch control system of the electronic portion of the printer;

FIGURES 11 and 12 are schematic diagrams which in conjunction with the voltage sensing circuit illustrated schematically in FIGURE 13, the cycle check circuit illustrated schematically in FIGURE 14, and the low voltage checking circuit illustrated schematically in FIG- URE 15, illustrate the control circuit of the printer;

FIGURES 16 and 17 illustrate diagrammatically the bail bar of the printer and the associated latch portion of the printer control circuit in the two static positions of the bail bar.

Referring now to the drawings in greater detail, a complete printer ltlti embodying the invention is generally comprised of three main portions: a mechanical portion, a power supply portion and an electronics portion, the latter portion cooperating with a computer-butler combination in supplying the various electronic control signals briefly referred to above and necessary for proper operation of the printer. The specific details of the mechanical portion of the printer are disclosed in application Serial No. 138,157 which is incorporated by reference. The subsequent description deals primarily with the electronics portion of the printer with the exception of the printer features shown in FIGURES 1-4.

Printer iii-t has a main frame 191 suitably configured to support the various mechanical, electromechanical and electro-optical components of the printer. The major components of the printer are mechanically synchronized by a suitable drive (not shown) deriving power from motor 107. The synchronously driven components include print drum 109 mounted on pivoted arm 273 and having longitudinal rows of raised characters 161. Sprocketed paper 157 is stepped by tractors 380 and 386 through a print station 159 (FIGURE 2) behind drum 199 and in front of inked ribbon 162 which is moved parallel to the axis of the drum through the print station.

A group of one hundred twenty hammers 166 are disposed behind ribbon 162 at the print station, and they are mounted in and constrained by ways 173 and 174 in guides 169 and 168. Each hammer has a print face 181 at one end, and a pivot at the opposite end. Interposer linkages are pivotally connected to the hammers, and each linkage (FIGURE 2) is made of a first link or beaver tail 182 pivoted to its hammer at one end and contacting an arm of a crank 223 at its opposite end. Crank 2.23 has three arms: arm 219 contacted by link 132, arm 225 which cooperates with bail bar 243 (described later) and a third arm to which armature 224 is fixed.

Electromagnets 226 (one for each hammer) are used to electrically address the hammers by attracting armatures 224 to pole pieces 227 or repelling the same while being aided by springs 186. These springs are attached at their upper ends by ball 135 and socket 184 connections to links 182, and at their lower ends to brackets 23%) to frame 1&1.

Cam 168 is driven by motor 107 at a predetermined speed, and its lobes 241 drive the addressed interposers in a manner to cause their hammers to impact the ribbon and paper against the characters of the print drum. More specifically, when a hammer is addressed, its interposer linkage is lowered, placing impact surface 18-3 of link 132 in the path of a cam lobe, e.g. lobe 241a. This lobe will then drive link 182 to the right (as shown in FIGURE 2) thereby driving its hammer into the print station. Hammer impact during printing will return the hammer and link 182, and meanwhile lobe 241]) will strike surface 242 of crank 2319, thereby restoring the interposer linkage to the rest (non-addressed) position.

The movement of ribbon 162 can be accomplished by ordinary means. However, paper 157 is stepped through distances equal to one or more print lines, upon command. Thus, paper tractors 380 and 336 are stepped by an electrical spring clutch 128 (described later) under the control of an electro-optical format control device 375. The format control is made of an optical tape reader for tape 429, and preferably uses a row of photodiodes 427 as the sensory elements.

While the mechanical timing as between the cam and the print drum are exact, it is also necessary that the electronics portion of the printer receive in advance s gnals as to what horizontal row of characters on the print drum is approaching the row of print hammers and that a lobe on the cam is approaching a position to strike the hammers that are next to be addressed. This is so that the computer-buffer and the electronics portion of the printer can generate and transmit the next set of signals necessary to address the proper hammers at the proper position and at the proper time.

The means, a code disk assembly 272 (FIGURE 1), employed for signaling which row of characters is approaching the print position, includes an optical code disc 31% driven with drum Hi9, together with an optical reader represented by lamp 34%) and lens 341.

The means for determining and signaling the position of the cam lobes 241 is shown in FIGURE 4. A nonmagnetic timing disk or wheel 265 is fixed to the reduced outer end of the shaft 266 of cam 108. Wheel 265 has soft iron or other elements 268 made of an electromagnetic material mounted in the outer periphery thereof so as to be at least partially exposed, these elements being equal in number and spaced circumferentially in substantially the same position as the cam lobes 241 are formed on the cam. Theoretically, lead time is required; this is factory adjusted by rotation of the wheel 265 on the shaft 26%, the adjustment possibly varying slightly with each printer and being essentially permanent.

A magnetic pickup unit 269 of any suitable design, such as the model 3015A magnetic pickup made and sold by Electro-Mation Company, is positioned adjacent the wheel 265. This is a standard commercially available item so that the constructional details need not be disclosed. Since a current is passed through the unit 269, a signal constituting a variation in current is produced whenever one of the magnetic elements 268 passes the magnetic pickup 259. These signals and their function are described in greater detail in the description of the electronics portion of the printer, it being sufiicient to state at this time that the signal indicating the position of a cam lobe is produced sufficiently in advance of actual hammer operation to enable the proper hammers to be addressed.

In order to prevent a meaningless line of print when the printer is initially energized (explained fully in application Serial No. 138,157) rotary bail bar 243 having cam surface 244, is mounted to span the interposer linkages. The bail bar is operated by conventional rotary solenoid 245 having a built-in return spring. When energized the solenoid rotates bail bar 2&3 to a position at which surface 244 bears against arms 225 of cranks 223, and when de-energized, the solenoid spring returns the bail bar to the position shown in FIGURE 2.

FIGURE 3 shows the positions of a number of switches, cg. switches 246 and 247 and latch solenoid 243. These together with other switches and solenoids (used mainly as interlocks) are also shown in the electrical and logic drawing figures, and they are described in more detail later.

The electronic portion Silt? of the printer includes a hammer control system 502, a hammer gate system 5% and a paper motion spring clutch control system 506. The hamm r control system Sit-2 illustrated in FIGURE 8 is provided to synchronize the operation or" the electronic portion of the printer with the mechanical portion thereof and to sequence the operation of the electronic portion of the printer. The hammer gate system 504 illustrated in FIGURE 9 is provided to prepare the selected printer hammers for actuation in accordance with signals fed to the printer by the computer 598. The paper motion spring clutch control system 5% illustrated in FIGURE 10 is provided to control the advance of paper through the printer in accordance with a predetermined format and to inhibit the input of information to be printed to the printer during paper advance.

The electronic portion Shit of the printer including the hammer control system 5%2, hammer gate system 5&4 and paper motion spring clutch control system see shown in block diagram in FIGURE 7 will be considered in detail after briefly considering the relation thereof to the computer 593 shown in block diagram in FIGURE 5 and the buffer 51% illustrated in block diagram in FIGURE 6.

As previously indicated the computer 598 provides both information and function input signals to the printer. The bufier 51b is provided between the computer 508 and the electronic portion 5% of the printer to permit use of the printer with the particular computer.

The computer 50% is conventional and includes a computer input-output buffer register 512, the memory systern 55h, instruction register 552, control system 55 and an arithmetic register 556 and suitable connections therebetween, as shown diagrammatically in the computer block diagram of FIGURE 14. The computer input and output buffer register 512 includes the computer printer select output conductors 514 and 516, the seven computer input conductors 518-524, the printer input request conductor 536, computer information ready conductor 538 and computer function ready conductor 54% connected thereto.

Since the computer 5% is conventional and forms no part of the present printer invention, it will not be considered in greater structural detail. However, the operation of the computer 5% will be considered briefly to indicate the connection of the printer of the invention thereto, through the buffer 519 and the related functioning thereof.

In operation the computer 5&8 may be connected through the computer input-output bufier register 512 to a number of different units, such as the printer of the invention, which units operate to program information to the computer or to receive computer outputs in the 1 l V manner of the printer of the invention either directly or through a butler, such as 51%. Therefore, a signal is produced on the conductors 514 and 516 by the computer when the printer is selected for use with the computer.

Before the printer is selected, however, information which it is desired to print with the printer and printer function information are first programmed into the computer 503 over the computer input conductors 518-524 from acomputer input unit, such as a magnetic tape reader (not shown). The computer Still stores the input information it receives over conductors 513-524 in the memory system 558'.

Subsequently the computer control system 554 under instructions from the instruction register 552 either on request from the printer over conductor 536 or independently due to programming operates on the stored input in formation in the arithmetic register 556 and feeds desired information and function signals to the printer through the butler 51% from the computer input-output buffer register 512 over computer output conductors 542-548, computer information ready conductor 538 and computer function ready conductor 549.

The butter 510, as previously indicated, performs the function of impedance matching and amplifying of signals passed directly between the printer and the computer 508. Additionally the buffer gates selected signals between computer EtES and the printer to insure their possible presence only during periods when the printer has been selected for operation with the computer. The buffer also provides a strobe signal to inhibit operation of the printer after information signals have been fed thereto until the information signals are stable. Further the bulfer Sit) functions to prevent resetting of the printer input flip-flops before the computer information is stablized thereon and has been used.

Thus the buffer 51% includes the printer input request line impedance matching pad and amplifier 5S8 positioned between the printer input request conductor 55% from the printer read out enable circuit are and the printer input request conductor 535 to the computer Similarly, the computer output lines impedance matching pads, amplifiers and inhibit gates 562 are provided in the buffer between the computer output conductors 542-548 and the printer input conductors 564-570, and the printer code disk character generator output circuit, impedance matching pads, amplifiers and inhibit gates are provided in the buffer 510 between the output conductors 586-592 from the print drum character generator photodiode system 272 of the printer and the input conductors 518-524 of the computer 588.

Gating of the computer output of the printer over computer output conductors 542-543, the printer paper advance gate system 596, the printer input flip-lop reset generator 598 and the print drum character generator photodiode system output over conductors sac-s 2 is accomplished through the printer select gate circuit 636 in conjunction with the computer printer select line amplihers and impedance matching pads 662 which. receive signals from the computer 533 over the conductors 514 and 516 which determine selection of the printer for use with the computer.

Computer information ready signals from the computer 598 on the output conductor 538 are fed through the computer information output synchronizing circuit 6&4, containing pulse forming, amplifying and impedance matching portions, to the print strobe generator 606 over conductor 698 which also includes pulse forming circuits and delay networks so that the signal delivered to the computer input decoding system 616 of the line printer over the conductor 612 is of the proper magnitude and shape. The signal provided on conductor 612 permits use of the signal inputs to the computer input decoding system 616 over conductors 564-579 only after the signal inputs thereto are stable.

The printer paper advance gate system 596 as previous- 1y indicated is provided with a gate signal from printer select gate system 6% over conductor 614. The printer paper advance gate system 5% is further provided with a paper advance signal from the computer 598 over conductor 5-34 and conductor 616. When the gate signal and paper advance signal are present on conductors 61.4 and 616 a paper advance command signal on output conductor e18 of the butter 61% is provided from the printer paper advance gate system 59-5 on receipt of a computer function ready signal from the computer 5&3 on conduc tor from the computer function output synchronizing circuit which includes amplifying and impedance matching portions.

The printer input flip-flop reset generator 598 provides a reset signal on conductor 62% for the printer input flipiiops of the computer input decoding system 619 after each piece of information from the computer, whether it be computer function as a paper advance command or information to be printed, has been utilized by the line printer. A reset signal is provided on conductor 624 when a signal from the computer information output synchronizing circuit 684 over conductor 636 or a signal from the computer function output synchronizing circuit 622 over conductor 633 is present on the reception of a gate signal from the printer select gate circuit 6% over conductor 64%). The reset signals are provided on the trailing edge of the signals from the computer information output synchronizing circuit 6% and the computer function output synchronizing circuit 622 so that the signals on the printer input flip-flops are stabilized and used before the flip-flops are reset.

The buffer 516 also forms no part of the present invention and will not therefore be considered in further detail. The buffer 516 like the computer 508 has been considered only to provide information as to the use made of the signals on the conductors are and ssssaz from the line printer and information as to the origin of signals on input conductors 554-579, 612, 624 and 618 to the line printer.

As shown in FIGURE 7 the hammer control system 592 includes the magnetic pickup unit 269, printer control timer 644, the type command generator and amplifier 646, and reset command generator and amplifier 648. The print control timer 644 in conjunction with the magnetic pickup 269 sequences the operation of the printer including the timing of read out enable signals and printer type and reset commands.

The hammer gate system 56M includes the computer input decoding system 610 and separate hammer gating circuits 656, best shown in FIGURE 9 for each of the 120 print hammers. In operation the hammer gate system receives information or function signals, and strobe and reset signals from the computer 508 through butter 51%. The hammer gate system decodes the information or function signals to determine which printer hammers are to be actuated or which function is to be performed, prepares the hammer gating circuits associated with the indicated printer hammers for firing on reception of a print command and after a print command resets the input decording system 610 to receive additional information from the computer 568.

The paper motion spring clutch control system 506 comrises the start paper advance generator 658 including a start paper advance delay one-shot multivibrator 799 and a high power circuit 792 shown in FIGURE 10, paper skip channel select circuit 666, vertical format control photodiode system 375, paper vertical format control circuit sd including a low power circuit 794 also shown in FIGURE 10, paper motion spring clutch assembly 128 and read out enable circuit 668. In operation, a signal is fed from the start paper advance generator 658 to the paper motion spring clutch assembly to energize the clutch and initiate paper advance motion. Signals from the com puter input decoding system 616 and the vertical format con rol photodiode system 375 are then compared in the "t3 paper skip channel select circuit 660 to provide a control signal for the paper vertical format control circuit 664 to deenergize the paper motion spring clutch assembly 128 at the proper time to skip a predetermined number of lines during paper advance. The signals from the start paper advance generator 658 and the paper vertical format control circuit 664 are also used to actuate the read out enable circuit 668 to prevent the printer from requesting input information from the computer during paper ad- Vance.

Hammer control system More specifically, the magnetic pickup unit 269 of the hammer control system 502 shown in FIGURE 8 is positioned adjacent the timing disk 265 which as previously indicated is mounted on the cam shaft 267, for rotation therewith. Magnetic pickup probes are known and consist of an electric coil 702 surrounding a magnetic core 7 04. The reluctance of the magnetic circuit of the magnetic core is varied each time a magnetic member in the periphery of the timing disk passes the core 794 to provide a pluse of electrical energy in the coil 702.

The speed of the timing disk is such that every 6.25 milliseconds an electric impulse is generated in coil 702 which is fed to the delay multivibrator 765. Multivibrator 706 provides an output from the true (T) side thereof to the prime (P) side of the type command control flipflop 768 and to the reset power amplifier 71% through inverter 712 for one-half of a millisecond. Zero power output from the true side of the type command control flipflop 7G3 and from reset power amplifier 71-1) is provided at this time so that power is removed from the collector of all thyristors 65% previously turned on due to signals from the computer input decoding system 610. All thyristors 656 are thus turned off or rendered non-conducting.

At the end of the one-half millisecond reset signal the one-shot multivibrator 706 is triggered by a signal on conductor 716 from the one-half-millisecond integral delay 718 to the prime side thereof to provide an output signal from the prime side thereof on the conductor 72% to the true side of the read out enable one-shot multivibrator 722. During the next two milliseconds the read out enable one-shoe multivibrator 722 produces a printer input request signal on the conductor 56% to indicate to the computer that the printer desires information during this two milliseconds.

As previously indicated during this two milliseconds the computer interrogates an entire bin of its memory sy tem to find all characters in a complete line of 120 characters which the printer indicates to the computer 508 that it is capable of printing at this time. The particular character to be printed during a complete 6.25 millisecond cycle will of course depend on the position of the printer print drum 109.

Also, during this two milliseconds the hammer gate system 504 is operable to provide turn on signals for the thyristors 650 associated with the pulse coils 229 at the hammer positions, of the possible 120 positions on a printed line, indicated by the computer a being the adresses of characters the printer is capable of printing, to prepare the particular thyristors 650 for heavy conduction through the pulse coils 229 in response to a type command signal.

After the two millisecond portion of a 6.25 millisecond cycle of the printer, the read out enable one-shot multivibrator 722 is pulsed on the prime side thereof by a signal on conductor 736 to turn otf the read out enable ignal to the computer over the conductor 560 and to pulse the type command control flip-flop 798 on the true side there of over the conductor 738. An output from the type command power amplifier 714 over the conductor 74% is thus provided causing heavy current conduction through the pulse coils 229 of all transistors 656 which were previously turned on during the two millisecond input request time.

As previously indicated the coils 229 when energized counteract the magnetic efiect of the coils 223 one of which is associated with each of the coils 229 which coils 228 are energized by a constant voltage over conductor 744. Thus the beaver tails of the printer hammers associated with the thyristors 659 which have previously been turned on are permitted to drop into the path of the cam whereby printing of all similar characters at predetermined addresses on a line is accomplished by the printer.

The energizing of the coils 229 and the printing of the characters at the indicated addresses is accomplished during the remaining 3.75 milliseconds of a 6.25 millisecond printer cycle. Thus as the magnetic pickup unit 269 senses the next magnetic element in the timing disk 265 corresponding to the next lobe of the cam a second pulse is applied to the delay reset bus control one-shot multivibrator 705 to again produce a one-half millisecond reset signal and the cycle is repeated to print the next character on the print drum 169.

Hammer gate system The hammer gate system 504 illustrated best in FIG- URE 9 comprises seven printer input flip-flops 746-752 and a strobe signal trigger, or print command circuit 754. Eight four input AND gates, only two of which, 756 and 758, are shown, are connected to the strobe trigger circuit 754 and to the flip-flops 746-743. Similarly, fifteen four input OR gates, only two of which, 760 and 762, are shown, are connected to the flip-flops 749-752.

The AND and OR gates combined in a double level gating system illustrated diagrammatically in FIGURE 9 define unique conditions representing each of the 120 character addresses or positions on a line of the printer. The output from a different pair of AND and OR gates, for example AND gate 75:? and OR 76d as shown are connected to the base circuit of each of the 120 thyristors 650 provided in conjunction with hammers 1-120 to permit turning on of the thyristors individually at desired times as previously indicated.

More specifically the seven flip-flops 746-752 receive signals from the computer 593 over butter output lines Sod-57 on their true side. The input to the prime side of the input flip-flops 746-752 is connected to the printer input flip-flop reset generator 598 over conductor 618 from the butter 51%.

Thus in operation during the two millisecond period when a printer read out enable signal is sent to the computer 508 from the print control timer 644, coded signals from the computer representing all the addresses of a particular character on a single line to be printed, which the line printer is capable of printing during the particular 6.25 millisecond cycle of operation are serially fed to the printer input flip-flops 746-752. A single set of signals arrives at the printer input flip-flops on investigation of each position in a single bin of the memory system of the computer 508, as previously indicated.

In between the separate sets of signals received from the computer the printer input flip-flops are reset by means of a reset signal fed to the prime side thereof over line 618 from the buffer 510. As previously indicated the strobe input signal from printer strobe generator 606 to the print command circuit 754 over conductor 764- is fed to the line printer after each set of input signals are fed thereto over conductors 564-570 and after the input flipflops 746-752 have become stable.

Each of the eight AND gates have four inputs thereto, as shown in FIGURE 9. Three of the inputs to the eight AND gates are from the printer input flip-flops 746-748. The other input signal to each of the eight AND gates is from the print command circuit 754. The printer logic is such that when the AND gates receive a signal from each of the four inputs thereto simultaneously the output of the AND gate is a positive ten volts. When any of the inputs to the AND gates is not present the output therefrom is zero volts.

Each of the OR gates similarly has four input signals thereto. The input signals to the OR gates are provided v v by the printer input flip-flops 749-752. Computer logic is such that when any of the inputs to an OR gate is present the output therefrom'is a positive ten volts. When there is no input signal on any of the input lines to an OR.

gate the output signal therefrom is zero volts.

Thus it can be seen that by connecting each of the eight AND gates to a thyristor input conductor 766 of fifteen of the 120 thyristors 659 and by connecting the output of each of the OR gates to the thyristor input conductor 76% of eight of the 120 thyristors 650 that 120 unique signals present at the printer input flip-flops 746-752 will provide an input to separate ones of the 120 thyristors 65% of ten volts over the input conductors 766 and zero volts over the input conductors 768 which is a necessary condition for turning on the thyristors 650 during the two milliseconds in each 6.25 milliseconds cycle of the printer during which printer input request or read out enable signals are sent to the computer 5%.

Each thyristor 654 is coupled to the outputs of the separate gates such as AND gate 756 and OR gate 766 as indicated in FIGURE 9 through a resistor 77% and capacitor 772 which operate in conjunction with the diode 774 and resistor 786 to provide a turn-on signal at the base of the thyristors 659.

Thus considering the operation of a particular thyristor 650, when the signal input to the printer input flip-flops 746-752 are such that a signal is provided on all four conductors to the AND gate 756 and no signals are prescut on the conductors to the OR gate 760 the capacitor 772 will be charged through resistor 770 due to the ten volt potential difference thereacross. The strobe signal applied through the print command circuit 7 54 is then removed from the AND gate 756 after the input flip-flops 746-752 are in a stable state. The voltage at AND gate 756 will therefore drop to zero volts and therefore the voltage at the thyristor goes negative causing the capacitor 772 to discharge through the diode 774 and thyristor 650 sufiicient to turn on the thyristor so that during the previously indicated subsequent 3.75 millisecond printer type command the thyristor 650 will conduct heavily through the pulse coil 229 associated therewith to cause printing of the character at the particular address indicated by the signal on printer input flip-flops 746-752.

The thyristor switching circuit as explained above has the advantage over a normal two transistor flip-flop of requiring less circuit components. Further the turnon time requirements of the pulse coil energizing circuit and the turn-on current are relatively critical in the printer and the thyristor switching circuit explained above meets these requirements.

Thus, in the printer the minimum time between character sensing as governed by the logic speed of the driving computer will be seven microseconds while the maximum switch time of the thyristor is .15 microseconds. This time differential-between. time available and time used in thyristor turn-on permits the use of a capacitor coupled thyristor input as described above wherein the input capacitor 772 is slowly charged during the two millisecond hammer selection portion of the 6.25 millisecond printer cycle and rapidly discharged at the end of the cycle if the thyristor associated therewith is turned on.

Further, with the thyristor hammer gate circuit, capacitive thyristor input and the double level gating described above, the power requirements of the printer of the invention are kept to a minimum so that maximum drive current required from any OR gate is the current necessary to charge eight 130 picofarad twenty kilo-ohm networks in six microseconds and the maximum current required from any AND gate is the sum of the current necessary to turn on one thyristor and the discharge current from fourteen thyristor resistance 'capactance input networks. The net result is a system of 120 medium current (450 milliamperes) pulse coils which may be actuated through a low level milli-amperes) gating system by high speed (one megacycle) low level (5 milli-amperes) inputs.

Paper motion spring clutch control system The paper motion spring clutch control system 506, as best shown in FIGURE 10, is provided to advance paper through the printer in response to paper advance signals from the butter 510 over conductor 618. The number of lines skipped during paper advance by the printer is controlled by the vertical format control photo diode system 375 previously considered, in conjunction with the computer 568. It will be understood that although the number of lines skipped is, in the present discussion, determined jointly by the vertical format control photodiode system 375 and the computer 503, complete control of the vertical format of the printer can be programmed into the printer.

The paper motion spring clutch control system 506 as previously indicated comprises a high power circuit 792 which initiates actuation of the clutch device 128, and a low power circuit 794 which sustains actuation of the clutch. A printer input request inhibit circuit 686, a stop paper advance circuit 798 and a start paper advance delay one-shot multivibrator 799 are also included in the system 506.

In the stop paper advance circuit 798 signals are received by the paper skip channel select circuit 660 over conductors 683-695 from the vertical format control photodiode system 37 5 and from the computer input decoding system 610 over conductors 681-688. On a preselected combination of the received signals the paper skip channel select circuit 660 provides an output signal on conductor 790 to cause disengagement of the clutch 128 as will later become obvious.

The high power separate clutch actuating circuit 792 includes the start paper advance one-shot multivibrator 899 and the high power paper drive amplifier 802 for energizing the power transistor 8% to cause a high current to be conducted through the paper motion spring clutch solenoid 414. The low power clutch actuating circuit 794 includes the paper drive format control flip-flop 8% and the low power paper drive amplifier 810 for energizing the power transistor 812 to cause current to be conducted through resistor 814 and the paper motion clutch solenoid 414 after transistor 804 is turned off. The printer input request inhibit circuit 686 includes the OR gate 816 and the printer input request inhibit one-shot multivibrator 818. It will be noted that the multivibrators 799, 800 and 818 include time delay circuits 820, 822, and 824, respectively, integrally associated therewith.

In operation the paper motion spring clutch control system 506 receives a start paper advance input signal from computer 508 over the conductor 618 from the buffer 510 after a line has been printed. The true side of the start paper advance delay multivibrator 799 is triggered by the signal from computer 508 and provides an output signal on conductor 827. to trigger the true side of multivibrator 8G8. Multivibratcr S00 is triggered on the true side by a signal from the true side of multivibrator 799 after a time delay of for example five milliseconds which is suificient to permit the mechanical portions of the printer to reach a static condition and prevent tearing of the printer paper. The time delay is diagrammatically indicated as delay 801.

In the high power circuit 792 for actuating the clutch solenoid 414 the output of the multivibrator 799 on conductor 326 is fed to the true side of the start paper advance multivibrator 800 to produce an output on conductor 834 which when amplified through the high power paper drive amplifier 802 will cause high conduction of the power transistor 804 to cause a high current to pass through the paper motion spring clutch solenoid 414. The input to the amplifier 802 over conduct-or 834 is'maint-ained for a period determined by the delay 822 which is an integral part of the multivibrator 806 after which it is stopped due to an input to the prime side of multivibrator 800.

Thus the major function of the high power clutch actuating circuit 792 is to provide a high current impulse 

1. A CONTROL SYSTEM FOR A PRINTER OF THE ROTATING DRUM TYPE WHEREIN THE PRINTER HAS AN ELEMENT WHICH ROTATES AT A SPEED CORRESPONDING TO THE DRUM AND WHEREIN THE PRINTER FURTHER HAS AN INDEPENDENT MECHANICAL PORTION INCLUDING SAID ELEMENT, AND AN ELECTRONIC PORTION OPERABLE INTERDEPENDENT MECHANICAL AND ELECTRONIC PORTIONS OPERABLE TO CYCLE THE ELECTRONIC PORTION OF THE PRINTER THROUGH RESET, READ AND TYPE COMMAND TIMES SEQUENTIALLY IN SYNCHRONISM WITH THE OPERATION OF THE MECHANICAL PORTION; SAID CONTROL SYSTEM COMPRISING SEPARATE PRINTER RESET, READ AND TYPE COMMAND BUSES, ELECTROMECHANICAL MEANS FOR PERIODICALLY PRODUCING AN ELECTRIC SYNCHRONIZING SIGNAL AT INTERVALS DETERMINED BY THE SPEED OF OPERATION OF SAID ELEMENT OF THE MECHANICAL PORTION OF THE PRINTER, MEANS CONNECTED TO SAID ELECTRO-MECHANICAL MEANS AND RESPONSIVE TO THE SYNCHRONIZING SIGNAL PRODUCED THEREBY FOR PRODUCING A RESET SIGNAL OUTPUT ON SAID RESET BUS FOR A PREDETERMINED TIME AFTER PRODUCTION OF A SYNCHRONIZING SIGNAL, MEANS CONNECTED TO THE MEANS FOR PRODUCING THE RESET SIGNAL AND RESPONSIVE TO TERMINATION OF THE RESET SIGNAL AFTER SAID PREDETERMINED TIME FOR PRODUCING A PRINTER READ SIGNAL ON SAID PRINTER READ BUS OF A SECOND PREDETERMINED DURATION, AND MEANS CONNECTED TO BOTH THE MEANS FOR PRODUCING A RESET SIGNAL AND THE MEANS FOR PRODUCING A PRINTER READ SIGNAL AND RESPONSIVE TO THE RESET SIGNAL AND READ SIGNAL FOR PRODUCING A TYPE COMMAND SIGNAL ON THE TYPE COMMAND BUS BETWEEN THE END OF THE PRINTER READ SIGNAL AND THE BEGINNING OF A SECOND RESET SIGNAL. 